GaAs Microisland Anodes Protected by Amorphous TiO₂ Films Mitigate Corrosion Spreading During Water Oxidation in Alkaline Electrolytes

Microisland structures of ∼200 μm diameter GaAs circles were fabricated and used to spatially isolate defects during electrochemical operation as an anode in aqueous alkaline electrolytes. The microisland structures allowed one to measure the rate and distribution of the pinhole formation on electrodes protected by 110 nm-thick amorphous titanium dioxide (a-TiO2) films formed by atomic layer deposition. Although no crystalline regions were detected by Raman spectroscopy, a limited number of defects were present in the a-TiO2 layer and developed into new microscopic pinholes within the first 20 h of electrochemical operation. The film dissolved at a rate of <13 nm per day, and hence, intrinsic film dissolution was not the primary mode of pinhole formation during this first 20 h of operation. The fabrication processes presented herein only utilized chemical etching and mechanical polishing and, consequently, should be readily transferable to the fabrication of the more complicated np+-GaAs structures.